How Natalie Portman nailed her Oscar-nominated performance as Jackie Kennedy

The hype for Natalie Portman's Oscar-nominated performance in "Jackie" came early.

Her stirring performance as First Lady Jacqueline Kennedy during the aftermath of the assassination of her husband JFK was the talk of the Toronto International Film Festival all the way back in September 2016, when many believe she would clinch the Oscar nod, which of course she did. She's now a frontrunner in the category.

Portman, who previously won an Oscar for her starring role in 2010's "Black Swan," has the look and unique voice of Kennedy down perfectly, which took a lot of preparation leading up to filming.

"I read every biography I could get my hands on," she told Business Insider. "And we recreated a lot of the White House tour for the film, so that was helpful to see how she walks and how she moves and her facial expressions."

The movie follows Kennedy as she recounts to a reporter the assassination and planning of her husband's funeral. But the movie also shows the different personas Kennedy had in front of different people — a debutante in public but feisty and no-nonsense behind closed doors.

Portman picked up on that in her research, which included listening to recorded interviews Kennedy did with biographer Arthur Schlesinger.

"When she was doing interviews, [her voice] was a lot more girly and soft, and then when you hear her talking to Schlesinger at home, you hear the ice in the glass clinking and the voice is a little deeper and her wit comes out more," Portman said. "So you get this real sense of the two sides."